The present invention relates to a method and to a system for reducing the risk of injury to the driver of a vehicle in the event of a head-on collision.
Essentially all cars are currently provided with steering wheel accommodated air bags with the intention of preventing injury to the driver.
However, an air bag is not able to absorb on its own the amount of energy required to arrest movement of an unbelted driver in the event of a head-on collision of, e.g., 50 km per hour. The air bag is intended to distribute the load uniformly over the head and chest of the driver, so that no part of the body will be subjected to local heavy loads. A major part of the kinetic energy concerned is normally absorbed in the steering wheel suspension. Vehicles fitted with air bags therefore have some form of collapsible steering wheel suspension, which is intended to collapse in a controlled manner so as not to exceed a chest acceleration limit of about 60 G.
In addition to being fitted with air bags, a number of vehicle models are also fitted with a so-called knee-bar structure. The knee-bar structure is intended to lessen the effects of hitting the underside of the instrument panel in the event of a head-on collision, and to absorb the kinetic energy of the lower part of the driver's body. The knee-bar is constructed so that the forces to which the driver's thighs are subjected will not exceed about 10 kN. The knee-bar is normally placed inwardly of the instrument panel or dashboard frame and is not therefore visible, said knee-bar normally being anchored in the vicinity of the steering wheel suspension.
The course of events that occur when the vehicle hits a barrier or is involved in a head-on collision can be described in the following way: When a vehicle hits a barrier, the front part of the vehicle will be deformed. The vehicle speed decreases at the same time as the driver continues to move essentially at the original, vehicle speed, causing the driver to gradually approach and finally reach the forwardly lying furnishings, i.e. the steering wheel suspension, steering wheel, air bag, and knee-bar. These components shall be dimensioned for controlled deformation, so as not to exceed the tolerance levels of the human body.
The characteristic that corresponds to front deformation of a vehicle is referred to in the art as the pulse of the vehicle. The pulse also describes the course of vehicle retardation during the collision. An aggressive pulse, i.e. a rigid front-part, results in marked retardation of the vehicle. A quiet, or peaceful, pulse, i.e. a soft front-part that has a long deformation distance, results in more gentle retardation. A quiet pulse is, of course, preferable with respect to those travelling in the vehicle, but results in a larger vehicle.
The worst collision sequence on the part of the driver is when the vehicle has stopped completely before the driver has begun to load the furnishings. This places a very high demand on the ability of the furnishing to absorb the kinetic energy of the driver. An optimal course of events can thus be described as one in which the driver is positioned so close to the furnishings as to load said furnishings initially prior to the crash or collision. The driver is then a part of the living mass of the vehicle and can thus avail himself/herself of the deformation zone of the front part of the vehicle as an extended braking distance, which reduces the loads.
A driver will be seated at roughly the same distance from the front furnishings irrespective of the size of the vehicle and consequently much greater demands are placed on the air bag system of a small car. Enhanced safety can be achieved by coupling or uniting the driver with the car as quickly as possible in the event of a collision, so as to limit the level of injuries sustained. Among other things, this requires a stable steering wheel suspension, so that a reaction force can be quickly built-up. When the steering suspension is too soft, it is able to deform without absorbing energy during the critical phase in which deformation of the car or vehicle is still in process. Another way of rapidly coupling the driver to the car is to use highly aggressive and hard air bags that will be inflated quickly and therewith quickly couple the driver to the car.
The majority of steering wheel suspension systems have a common mode of behaviour which dramatically influences the function of the system in a virtual traffic environment.
When an unbelted driver reaches the front furnishings during a collision, it is the driver's knees that first come into contact with said furnishings, due to the fact that the driver's knees are usually those parts of his/her body that are located closest to the furnishings. When the knees exert force on the knee-bar, the bar forces up the steering wheel suspension, which, in turn, means that the steering wheel is pressed angularly upwards and away from the driver's chest. When the driver then loads the air bag, the driver and the steering wheel will have assumed a highly unfavourable angle, causing the driver to load the lower part of the steering wheel in the absence of any appreciable part of the air bag between him and the steering wheel. This phenomenon has two negative effects. Contact of the driver with the air bag results in that the pulse can no longer be utilized and in the steering wheel taking an unfavourable angle in relation to the driver's body. This effect is currently compensated for by making the air bag larger and more aggressive.
This problem has been observed in American studies on accidents involving cars equipped with air bags. Head injuries are reduced whereas breast injuries caused by the lower part of the steering wheel dominate.
Three parallel conditions have been tested in other tests, an unbelted driver with air bag, three-point safety harness and air bag, and solely a lap belt and air bag. The results showed that the best combination is the lap-belt and crash-bag combination, which resulted in the least injuries. The combination that includes a three-point harness is too rigid, since the air bag is optimised in respect of an unbelted driver. When solely a lap belt is used, the knees are unable to press forward the conventional steering wheel suspension and angle the steering wheel upwards, wherewith the hip-belt and crash-bag combination functions best due to this fact. The trials also showed that current air bags are not at all optimised towards a person wearing a three-point belt.
Another problem that occurs when the steering wheel suspension and the steering wheel are angled upwards is that the ability of the steering wheel suspension to absorb kinetic energy diminishes. The regulated collapse of the steering wheel suspension in the direction of car movement is influenced by the application of further deformation.
The problems associated with current steering wheel suspensions can be summarised as follows:
Impact of the knees with the knee-bar causes the steering wheel to be angled upwards, therewith limiting the protection afforded by the air bag in the lower part of the steering wheel. The steering wheel suspension must be strengthened, which increases both costs and weight. The absorption of energy offered by the steering wheel suspension in an axial direction has a limited effect, since as a result of this angling of the steering wheel the actual load does not act axially. Current crash-bag systems are optimised with respect to unbelted drivers. The air bags are often overdimensioned.
The introduction of fewer movable parts and therewith limitation of the steering wheel adjustment facilities is liable to result in the steering wheel moving further away from the driver and its upward angle reduced. It is therefore normal for current day steering wheel suspension systems intended for steering wheels that incorporate an air bag to lack adjustment facilities.